1. Field of the Invention
The present invention generally relates to a method for fabricating micromagnetic, microelectronic or micro-optical devices or components on a substrate. More specifically, the present invention relates to a chemical-mechanical etch (CME) method for patterned etching of a substrate surface.
2. Description of the Related Art
Various etching techniques are used in the fabrication of various microminiature structures and devices to form patterns in a substrate for many applications. An etching technique which is suitable for a particular purpose etches selected layers in a structure without damaging other layers and forms structures with a sufficient etch rate, etch rate selectivity and directional selectivity that a specified end product is produced efficiently.
A wet etching technique employs liquid chemicals, such as acids or corrosive materials, as an etching agent. The etching process proceeds through chemical reactions at the surface of the etched material and is limited by the rate of chemical reactions and the rate of removal of products of the chemical reaction. In some applications the wet etching process is electrically aided by connecting the structure to be etched either an anode or a cathode of an electrolytic cell. Unfortunately, wet etching has several disadvantages. Direction etch selectivity is typically very poor for wet etchants. One result of this poor direction etch sensitivity is a large line-width loss that precludes the usage of wet etching to form narrow lines that are common in many applications. Furthermore, the etch rate is only marginally controllable for many wet etchants. A further disadvantage is that wet etching requires the handling, use and disposal of highly toxic and corrosive chemicals, raising cost and safety concerns.
An alternative type of etching is dry etching, or plasma-assisted etching, which uses either chemical or physical reactions between a low-pressure plasma or glow discharge and the surface to be etched in a gas phase. Dry etching is a complex process with results that are greatly affected by small variations in process parameters. Dry etching typically is used to pattern smaller geometries than wet etching and has lateral etch rates that are small so that the etched pattern is highly controllable and smooth edge profiles are produced. Advantages of dry etching are a highly directional etch anisotropy and a facility to penetrate small photoresist apertures for etching small and intricate geometries.
Plasma etching is a process in which a plasma generates reactive species that chemically etch material in direct proximity with the plasma. Plasma etching is typically used to etch photoresists, silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum, polysilicon and metal silicides. If the chemical reactions are enhanced by the kinetic energy of the ions in the plasma, the process is a kinetically-assisted chemical reaction. Reactive ion etching is similar to plasma etching but only uses kinetically-assisted chemical etching. Reactive ion beam etching separates the wafers from the plasma by a grid that accelerates the ions created in the plasma towards the wafer, raising the ion energy so that some etching is caused by physical reactions.
Sputter etching uses energetic ions from the plasma to physically wrench (sputter) atoms from the substrate surface without assistance by chemical reactions.
Ion milling is a purely mechanical etching method that uses a roughly collimated beam of energetic ions to erode a surface by bombardment. Ion milling advantageously can be applied at angles other than an angle perpendicular to the substrate wafer.
The etch rate achieved by the various etching techniques is widely variable depending on the characteristics of the material to be etched and etchant characteristics such as the selected chemical for chemical etching methods and the ion, energy and density of the etching ions for ion etching methods. Typical etch rates are in the range of 100 to 3000 xc3x85/min for most materials.
Some materials are not easily etched in a desired pattern using conventional etching methods. For example, various substrates resist etching using conventional patterned etching methods such as plasma etching. Chemical etching is not easily performed due to the usage of toxic chemicals and the poor directional selectivity of chemical etchants.
What is needed is a technique for etching hard materials that yields a rapid but controllable etch rate and directionality. What is also needed is an etching technique for hard materials that has high direction selectivity.
It has been discovered that chemical-mechanical processing of a patterned substrate is highly effective for selectively etching patterned portions of the substrate surface, producing deep narrow features with a rapid etch rate. This chemical-mechanical processing is termed chemical-mechanical etching and produces a result that is substantially the opposite of the planarization that is achieved by conventional chemical-mechanical polishing (CMP). Chemical-mechanical etching is useful for patterned etching of substrate materials including, for example, silicon, silicon dioxide, silicon nitride, gallium arsenide, polyimide, photoresist, aluminum, tungsten, molybdenum, titanium, glass, and the like.
In accordance with the present invention, a chemical-mechanical polishing (CMP) technique which is widely used for planarization of surfaces is converted for usage as an etching technique, more specifically a chemical-mechanical etching (CME) technique, by forming a patterned mask on the substrate surface prior to mechanical polishing. The usage of chemical-mechanical polishing techniques in this manner yields a surprisingly effective etching method with highly desirable properties including a rapid etch rate, a highly controllable etch rate, a highly controllable etch depth, and a greatly selective etch directionality.
In accordance with an embodiment of the present invention, a coating that inhibits the removal of the substrate material protects selectively patterned areas of a substrate, thereby creating a recess in substrate areas that are not protected by the coating.
In accordance with a specific embodiment of the present invention, a substrate is patterned with a diamond-like carbon (DLC) coating and etched using a chemical-mechanical etch (CME) process. The CME process forms deep narrow features having an angle essentially normal to the plane of the substrate surface.
Many advantages are achieved using the disclosed chemical-mechanical etch (CME) process. One advantage is that the CME process performs a highly anisotropic etch that forms sidewalls of an etched cut that are essentially vertical. Another advantage is that the CME process forms a highly controllable structure with substantially no undercutting of the mask. It is advantageous that the etch rate is relatively rapid (for example, approximately 1 xcexcm per minute) so that processing throughput is facilitated, but also sufficiently linear and restrained so that precise control of the etch depth is facilitated.
Another advantage is that the usage of toxic and dangerous chemicals is avoided, thereby lowering processing costs and improving safety.